Biofilm bacterial communities in urban drinking water distribution systems transporting waters with different purification strategies

Impacts of water treatments on bacterial communities of biofilm and loose deposits in drinking water distribution systems

Treated drinking water is delivered to customers through drinking water distribution systems (DWDSs). Although studies have focused on exploring the microbial ecology of DWDSs, knowledge about the effects of different water treatments on the bacterial community of biofilm and loose deposits in DWDS is limited. This study assessed the effects of additional treatments on the bacterial communities developed in 10 months' old pilot DWDSs. The results showed a similar bacterial community in the pipe-wall biofilm, which was dominated by Novosphingobium spp. (20-82 %) and Sphingomonas spp. (11-53 %), regardless of the treatment applied. The bacterial communities that were retained in the distribution systems (including pipe-wall biofilm and loose deposits) were similar to the particle-associated bacteria (PAB) in the corresponding supply water. The additional treatments showed clear effects of the removal and/or introduction of particles. The genera Aeromonas spp., Clostridium spp., Legionella spp., and Pseudomonas spp., which contain opportunistic pathogenic species, were only detected among the PAB in ion exchange system. Our study demonstrated that the biofilm community is consistent across treatments, and the contribution from bacteria in loose deposits is important but can be controlled by removing particles. These findings offer more insight into the origin and development of microbial ecology in DWDSs and suggest paths for further research on the possibility of managing the microbial ecology in distribution systems.

Influence of drinking water biofilm microbiome on water quality: Insights from a real-scale distribution system

Biofilms, constituting over 95 % of the biomass in drinking water distribution systems, form an ecosystem impacting both the aesthetic and microbiological quality of water. This study investigates the microbiome of biofilms within a real-scale drinking water distribution system in eastern Spain, utilizing amplicon-based metagenomics. Forty-one biofilm samples underwent processing and sequencing to analyze both bacterial and eukaryotic microbiomes, with an assessment of active biomass. Genus-level analysis revealed considerable heterogeneity, with Desulfovibrio, Ralstonia, Bradyrhizobium, Methylocystis, and Bacillus identified as predominant genera. Notably, bacteria associated with corrosion processes, including Desulfovibrio, Sulfuricella, Hyphomicrobium, and Methylobacterium, were prevalent. Potentially pathogenic bacteria such as Helicobacter, Pseudomonas, and Legionella were also detected. Among protozoa, Opisthokonta and Archaeplastida were the most abundant groups in biofilm samples, with potential pathogenic eukaryotes (Acanthamoeba, Naegleria, Blastocystis) identified. Interestingly, no direct correlation between microbiota composition and pipe materials was observed. The study suggests that the usual concentration of free chlorine in bulk water proved insufficient to prevent the presence of undesirable bacteria and protozoa in biofilms, which exhibited a high concentration of active biomass.

A review of research advances on disinfection strategies for biofilm control in drinking water distribution systems

The presence of biofilms in drinking water distribution systems (DWDS) is responsible for water quality deterioration and a possible source of public health risks. Different factors impact the biological stability of drinking water (DW) in the distribution networks, such as the presence and concentration of nutrients, water temperature, pipe material composition, hydrodynamic conditions, and levels of disinfectant residual. This review aimed to evaluate the current state of knowledge on strategies for DW biofilm disinfection through a qualitative and quantitative analysis of the literature published over the last decade. A systematic review method was performed on the 562 journal articles identified through database searching on Web of Science and Scopus, with 85 studies selected for detailed analysis. A variety of disinfectants were identified for DW biofilm control such as chlorine, chloramine, UV irradiation, hydrogen peroxide, chlorine dioxide, ozone, and others at a lower frequency, namely, electrolyzed water, bacteriophages, silver ions, and nanoparticles. The disinfectants can impact the microbial communities within biofilms, reduce the number of culturable cells and biofilm biomass, as well as interfere with the biofilm matrix components. The maintenance of an effective residual concentration in the water guarantees long-term prevention of biofilm formation and improves the inactivation of detached biofilm-associated opportunistic pathogens. Additionally, strategies based on multi-barrier processes by optimization of primary and secondary disinfection combined with other water treatment methods improve the control of opportunistic pathogens, reduce the chlorine-tolerance of biofilm-embedded cells, as well as decrease the corrosion rate in metal-based pipelines. Most of the studies used benchtop laboratory devices for biofilm research. Even though these devices mimic the conditions found in real DWDS, future investigations on strategies for DW biofilm control should include the validity of the promising strategies against biofilms formed in real DW networks.

Bacterial communities of planktonic bacteria and mature biofilm in service lines and premise plumbing of a Megacity: Composition, Diversity, and influencing factors

Although simulated studies have provided valuable knowledge regarding the communities of planktonic bacteria and biofilms, the lack of systematic field studies have hampered the understanding of microbiology in real-world service lines and premise plumbing. In this study, the bacterial communities of water and biofilm were explored, with a special focus on the lifetime development of biofilm communities and their key influencing factors. The 16S rRNA gene sequencing results showed that both the planktonic bacteria and biofilm were dominated by Proteobacteria. Among the 15,084 observed amplicon sequence variants (ASVs), the 33 core ASVs covered 72.8 %, while the 12 shared core ASVs accounted for 62.2 % of the total sequences. Remarkably, it was found that the species richness and diversity of biofilm communities correlated with pipe age. The relative abundance of ASV2 (f_Sphingomonadaceae) was lower for pipe ages 40-50 years (7.9 %) than for pipe ages 10-20 years (59.3 %), while the relative abundance of ASV10 (f_Hyphomonadaceae) was higher for pipe ages 40-50 years (19.5 %) than its presence at pipe ages 20-30 years (1.9 %). The community of the premise plumbing biofilm had significantly higher species richness and diversity than that of the service line, while the steel-plastics composite pipe interior lined with polyethylene (S-PE) harbored significantly more diverse biofilm than the galvanized steel pipes (S-Zn). Interestingly, S-PE was enriched with ASV27 (g_Mycobacterium), while S-Zn pipes were enriched with ASV13 (g_Pseudomonas). Moreover, the network analysis showed that five rare ASVs, not core ASVs, were keystone members in biofilm communities, indicating the importance of rare members in the function and stability of biofilm communities. This manuscript provides novel insights into real-world service lines and premise plumbing microbiology, regarding lifetime dynamics (pipe age 10-50 years), and the influences of pipe types (premise plumbing vs. service line) and pipe materials (S-Zn vs. S-PE).

Recent advances in the unlined cast iron pipe scale characteristics, cleaning techniques and harmless disposal methods: An overview

Drinking water discoloration and its potential health risks (e.g., heavy metals, pathogens, carcinogenic organics) have aroused wide public concerns around the world, and the characteristics and corresponding cleaning techniques of pipe scales are one of the most important research fields closely related to people's lives and health. This Overview Article summarizes the latest research achievements about the new insights into the unlined cast iron pipe corrosion scale characteristics as well as the advanced cleaning techniques applied in drinking water distribution systems. The typical pollutants such as heavy metal ions, pathogens and disinfection by-products (DBPs) in pipe scales and the main cleaning techniques including unidirectional flushing (UDF), air scouring, ice pigging and guided ultrasonic waves (GUW) are categorized and elaborated. In the final part, the current challenges and future opportunities are also further discussed from the viewpoint of evolution process of pipe scales as well as the widespread application of advanced cleaning techniques. Moreover, the possible technical route for the innocent treatment and resource utilization of pipe scale waste is also proposed. It is anticipated that this review will attract more attention toward the in-depth study of pipe scales and their cleaning techniques to enjoy cleaner and healthier drinking water for people.

Microbiomes in drinking water treatment and distribution: A meta-analysis from source to tap

A meta-analysis of existing and available Illumina 16S rRNA datasets from drinking water source, treatment and drinking water distribution systems (DWDS) were collated to compare changes in abundance and diversity throughout. Samples from bulk water and biofilm were used to assess principles governing microbial community assembly and the value of amplicon sequencing to water utilities. Individual phyla relationships were explored to identify competitive or synergistic factors governing DWDS microbiomes. The relative importance of stochasticity in the assembly of the DWDS microbiome was considered to identify the significance of source and treatment in determining communities in DWDS. Treatment of water significantly reduces overall species abundance and richness, with chlorination of water providing the most impact to individual taxa relationships. The assembly of microbial communities in the bulk water of the source, primary treatment process and DWDS is governed by more stochastic processes, as is the DWDS biofilm. DWDS biofilm is significantly different from bulk water in terms of local contribution to beta diversity, type and abundance of taxa present. Water immediately post chlorination has a more deterministic microbial assembly, highlighting the significance of this process in changing the microbiome, although elevated levels of stochasticity in DWDS samples suggest that this may not be the case at customer taps. 16S rRNA sequencing is becoming more routine, and may have several uses for water utilities, including: detection and risk assessment of potential pathogens such as those within the genera of Legionella and Mycobacterium; assessing the risk of nitrification in DWDS; providing improved indicators of process performance and monitoring for significant changes in the microbial community to detect contamination. Combining this with quantitative methods like flow cytometry will allow a greater depth of understanding of the DWDS microbiome.

Variation in the Structure and Composition of Bacterial Communities within Drinking Water Fountains in Melbourne, Australia

Modern drinking water distributions systems (DWDSs) have been designed to transport treated or untreated water safely to the consumer. DWDSs are complex environments where microorganisms are able to create their own niches within water, biofilm or sediment. This study was conducted on twelve drinking fountains (of three different types, namely types A, B and C) within the Melbourne (Australia) city area with the aim to (i) characterize the water quality and viable and total counts at each fountain, (ii) compare the differences in the structure and diversity of the bacterial community between bulk water and biofilm and (iii) determine differences between the bacterial communities based on fountain type. Samples of water and biofilm were assessed using both culture-dependent and culture-independent techniques. Heterotrophic plate counts of water samples ranged from 0.5 to 107.5 CFU mL−1, and as expected, total cell counts (cells mL−1) were, on average, 2.9 orders of magnitude higher. Based on the mean relative abundance of operational taxonomic units (OTUs), ANOSIM showed that the structure of the bacterial communities in drinking water and biofilm varied significantly (R = 0.58, p = 0.001). Additionally, ANOSIM showed that across fountain types (in water), the bacterial community was more diverse in fountain type C compared to type A (p < 0.001) and type B (p < 0.001). 16S rRNA next-generation sequencing revealed that the bacterial communities in both water and biofilm were dominated by only seven phyla, with Proteobacteria accounting for 71.3% of reads in water and 68.9% in biofilm. The next most abundant phylum was Actinobacteria (10.4% water; 11.7% biofilm). In water, the genus with the highest overall mean relative abundance was Sphingomonas (24.2%), while Methylobacterium had the highest mean relative abundance in biofilm samples (54.7%). At the level of genus and higher, significant differences in dominance were found across fountain types. In water, Solirubrobacterales (order) were present in type C fountains at a relative abundance of 17%, while the mean relative abundance of Sphingomonas sp. in type C fountains was less than half that in types A (25%) and B (43%). In biofilm, the relative abundance of Sphingomonas sp. was more than double in type A (10%) fountains compared to types B (4%) and C (5%), and Sandarakinorhabdus sp. were high in type A fountains (6%) and low in types B and C (1%). Overall this research showed that there were significant differences in the composition of bacterial communities in water and biofilm from the same site. Furthermore, significant variation exists between microbial communities present in the fountain types, which may be related to age. Long-established environments may lead to a greater chance of certain bacteria gaining abilities such as increased disinfection resistance. Variations between the structure of the bacterial community residing in water and biofilm and differences between fountain types show that it is essential to regularly test samples from individual locations to determine microbial quality.

The role of antibiotics and heavy metals on the development, promotion, and dissemination of antimicrobial resistance in drinking water biofilms

Antimicrobial resistance (AMR), as well as the development of biofilms in drinking water distribution systems (DWDSs), have become an increasing concern for public health and management. As bulk water travels from source to tap, it may accumulate contaminants of emerging concern (CECs) such as antibiotics and heavy metals. When these CECs and other selective pressures, such as disinfection, pipe material, temperature, pH, and nutrient availability interact with planktonic cells and, consequently, DWDS biofilms, AMR is promoted. The purpose of this review is to highlight the mechanisms by which AMR develops and is disseminated within DWDS biofilms. First, this review will lay a foundation by describing how DWDS biofilms form, as well as their basic intrinsic and acquired resistance mechanisms. Next, the selective pressures that further induce AMR in DWDS biofilms will be elaborated. Then, the pressures by which antibiotic and heavy metal CECs accumulate in DWDS biofilms, their individual resistance mechanisms, and co-selection are described and discussed. Finally, the known human health risks and current management strategies to mitigate AMR in DWDSs will be presented. Overall, this review provides critical connections between several biotic and abiotic factors that influence and induce AMR in DWDS biofilms. Implications are made regarding the importance of monitoring and managing the development, promotion, and dissemination of AMR in DWDS biofilms.

Genomic Analysis and Stability Evaluation of the Phenol-Degrading Bacterium Acinetobacter sp. DW-1 During Water Treatment

Phenol is a toxic organic molecule that is widely detected in the natural environment, even in drinking water sources. Biological methods were considered to be a good tool for phenol removal, especially microbial immobilized technology. However, research on the “seed” bacteria along with microbial community analysis in oligotrophic environment such as drinking water system has not been addressed. In this study, Acinetobacter sp. DW-1 with high phenol degradation ability had been isolated from a drinking water biofilter was used as seeded bacteria to treat phenol micro-polluted drinking water source. Meanwhile, the whole genome of strain DW-1 was sequenced using nanopore technology. The genomic analysis suggests that Acinetobacter sp. DW-1 could utilize phenol via the β-ketoadipate pathway, including the catechol and protocatechuate branches. Subsequently, a bio-enhanced polyhedral hollow polypropylene sphere (BEPHPS) filter was constructed to investigate the stability of the seeded bacteria during the water treatment process. The denatured gradient gel electrophoresis (DGGE) profile and the quantification of phenol hydroxylase gene results indicate that when the BEPHPS filter was operated for 56 days, Acinetobacter sp. was still a persistent and competitive bacterium in the treatment group. In addition, 16S rRNA gene amplicon sequencing results indicate that Acinetobacter sp., as well as Pseudomonas sp., Nitrospira sp., Rubrivivax sp. were the predominant bacteria in the treatment group, which were different from that in the CK group. This study provides a better understanding of the mechanisms of phenol degradation by Acinetobacter sp. DW-1 at the gene level, and provides new insights into the stability of seeded bacteria and its effects on microbial ecology during drinking water treatment.

Microbial communities of biofilms developed in a chlorinated drinking water distribution system: A field study of antibiotic resistance and biodiversity

Antibiotic resistance and biodiversity were investigated in microbial communities attached to inner surfaces of water supply fittings in a chlorinated drinking water distribution system (DWDS) supplied by two independent water treatment plants (WTPs) drawing the same source water. The investigation of the effect of the season, the applied water treatment technology, and type, material, and age of water supply fittings on both antibiotic resistance and biodiversity in biofilms involved collection of tubercles during summer and winter seasons throughout the DWDS. A total of 16 samples were collected (8 per season) from areas supplied by two independent WTPs. Culturable aerobic antibiotic resistant bacteria (ARB) proved more prevalent in summer. Various antibiotic resistance genes (ARGs) were detected, confirming the role of biofilms as ARGs reservoirs, but the abundances of quantified genes (sulI, ermB, qacEΔ1, intI1) were low (a range of <LOQ to 2313 gene copies/mg dry mass of tubercles) throughout the DWDS. In terms of microbial community composition, Proteobacteria were dominant in each sample (51.51-97.13%), and the most abundant genus was Desulfovibrio (0.01-66.69%) belonging to sulphate-reducing bacteria. Biodiversity of microbial communities was shaped by many coexisting factors, including season, water supply fitting material, and sampling site location. Spatial distribution analysis revealed that although only samples collected at the same sampling sites were similar to each other in terms of antibiotic resistance, some samples collected in the close proximity were similar in terms of biodiversity. This suggests that antibiotic resistance spreads only locally over small distances in drinking water biofilms. Although actual drinking water biofilms have been previously investigated in terms of microbial biodiversity, this is the first study that characterised both antibiotic resistance and biodiversity of microbial communities attached to inner surfaces of a real DWDS functioning for decades.

Large-scale pattern of resistance genes and bacterial community in the tap water along the middle and low reaches of the Yangtze River

Antibiotic and metal resistance genes (ARGs and MRGs) in tap water are of great public health concern. However, very fewer studies focused on the relationship between resistance genes and opportunistic pathogens in tap water. In this study, the diversity and abundance of resistance genes and bacterial community from tap water at a large-scale along the middle and lower reaches of the Yangtze River were investigated. The total relative abundances of ARGs and MRGs were 2.95 × 10^-3-1.22 × 10^-1 and 1.93 × 10^-3-1.20 × 10^-1 copies/16S rRNA, respectively. The bla_TEM and merP detected were major ARG and MRG subtypes, respectively. Mobile genetic elements (Intl1 and tnpA) showed significant correlations with the abundance of ARGs. Heavy metals also played a vital role in the co-selection of ARGs. Surprisingly, there were still eight opportunistic pathogens in tap water, among which Escherichia coli, Helicobacter pylori, Mycoplasma pneumoniae, and Porphyromonas gingivalis were the potential host of ARGs and MRGs. Escherichia coli had the highest abundance, while Bacillus anthracis had the highest detected frequency (100%), a widespread opportunistic pathogen in tap water.

Biofilms in premise plumbing systems as a double-edged sword: microbial community composition and functional profiling of biofilms in a tropical region

To understand distributions of opportunistic premise plumbing pathogens (OPPPs) and microbial community structures governed by sample location, pipe materials, water temperature, age of property and type of house, 29 biofilm samples obtained from faucets, pipes, and shower heads in different households in Singapore were examined using next-generation sequencing technology. Predictive functional profiling of the biofilm communities was also performed to understand the potential of uncultivated microorganisms in premise plumbing systems and their involvement in various metabolic pathways. Microbial community analysis showed Proteobacteria, Bacteroidetes, Acidobacteria, Nitrospira, and Actinobacteria to be the most abundant phyla across the samples which was found to be significantly different when grouped by age of the properties, location, and the type of house. Meanwhile, opportunistic premise plumbing pathogens such as Mycobacterium, Citrobacter, Pseudomonas, Stenotrophomonas, and Methylobacterium were observed from the samples at 0.5% of the total reads. Functional prediction using 16S gene markers revealed the involvement of the biofilm communities in different metabolic pathways like nitrogen metabolism, biodegradation of xenobiotics, and bacterial secretion implying diverse functionalities that are yet to be studied in this environment. This study serves as a preliminary survey on the microbial communities harboring premise plumbing systems in a tropical region like Singapore.

Response of the Bacterial Community and Antibiotic Resistance in Overnight Stagnant Water from a Municipal Pipeline

Although drinking water safety has raised considerable concern, to date, the hidden health risks in newly released overnight water from a municipal pipeline have seldom received attention. In this study, bacterial community composition and the response of antibiotic-resistant bacteria (ARB) to ciprofloxacin, azithromycin, tetracycline, penicillin, and cephalosporin in overnight stagnant water were analyzed. With increases in heterotrophic bacteria plate count (HPC) during water stagnation, the numbers of ARB and the ARB/HPC ratios for the five antibiotics in resident water were observed to increase, which illustrated that the prevalence of ARB rose in the pipe network water during stagnation time (ST). Furthermore, during water stagnation for 12 h, an increase in bacteria related to fermentation was also observed. When the ST rose to 48 h, the fermentation bacteria become non-significant, and this was related to the exchange of pipe network water during daytime stagnation within the 48-h period. The antibiotic resistance index (ARI) showed that tetracycline had the highest resistance level in fresh water, and then decreased during water stagnation. When ST increased to 12 h, all ARI values of the five antibiotics were low, which was associated with changes in parameters during water retention and reduced resistance during short-term stagnation. When the ST increased to 24 and 48 h, the resistance to most antibiotics (except for tetracycline) increased, which showed that increasing antibiotic resistance is caused by the formation of biofilms in the pipeline during water stagnation.

Assessing the transition effects in a drinking water distribution system caused by changing supply water quality: an indirect approach by characterizing suspended solids

Worldwide, it is common that the drinking water distribution systems (DWDSs) may be subjected to changes of supply water quality due to the needs of upgrading the treatment processes or switching the source water. However, the potential impacts of quality changed supply water on the stabilized ecological niches within DWDSs and the associated water quality deterioration risks were poorly documented. In the present study, such transition effects caused by changing the supply water quality that resulted from destabilization of biofilm and loose deposits in DWDS were investigated by analyzing the physiochemical and microbiological characteristics of suspended particles before (T₀), during (T_3-weeks) and after upgrading the treatments (T_6-months) in an unchlorinated DWDS in the Netherlands. Our results demonstrated that after 6 months' time the upgraded treatments significantly improved the water quality. Remarkably, water quality deterioration was observed at the initial stage when the quality-improved treated water distributed into the network at T_3-weeks, observed as a spike of total suspended solids (TSS, 50-260%), active biomass (ATP, 95-230%) and inorganic elements (e.g. Mn, 130-250%). Furthermore, pyrosequencing results revealed sharp differences in microbial community composition and structure for the bacteria associated with suspended particles between T₀ and T_3-weeks, which re-stabilized after 6 months at T_6-months. The successful capture of transition effects was especially confirmed by the domination of Nitrospira spp. and Polaromonas spp. in the distribution system at T_3-weeks, which were detected at rather low relative abundance at treatment plant. Though the transitional effects were captured, this study shows that the introduction of softening and additional filtration did not have an effect on the water quality for the consumer which improved considerably after 6-months' period. The methodology of monitoring suspended particles with MuPFiSs and additional analysis is capable of detecting transitional effects by monitoring the dynamics of suspended particles and its physiochemical and microbiological composition.

Composition and Dynamics of Bacterial Communities in a Full-Scale Mineral Water Treatment Plant

The aim of this study was to gain insight into the bacterial composition and dynamics in a mineral water treatment system (MWTS). The bacterial community of a full-scale mineral water treatment plant in the Maofeng Mountain, South China, was studied using high-throughput sequencing combined with cultivation-based techniques in both the dry and wet season. Overall, adenosine tri-phosphate (ATP) concentration (6.47 × 10^-11 – 3.32 × 10^-8 M) and heterotrophic plate counts (HPC) (3 – 1.29 × 10³ CFU/mL) of water samples in the wet season were lower than those (ATP concentration 5.10 × 10^-11 – 6.96 × 10^-8 M, HPC 2 – 1.97 × 10³ CFU/mL) in the dry season throughout the whole MWTS. The microbial activity and biomass of water samples obviously changed along with treatment process. All 300 isolates obtained using cultivation-based techniques were distributed in 5 phyla, 7 classes, and 19 genera. Proteobacteria accounted for 55.7% (167) of the total isolates, among which predominant genus was Pseudomonas (19.3%). Illumina sequencing analysis of 16s rRNA genes revealed 15 bacterial phyla (relative abundance >0.1%) as being identified in all water samples. Among these, Proteobacteria constituted the dominant bacteria microbiota in all water samples. A large shift in the proportion of Bacteroidetes, Actinobacteria, and Firmicutes was obtained during the treatment process, with the proportion of Bacteroidetes, Actinobacteria decreasing sharply, whereas that of Firmicutes increased and predominated in the final water product. The core microbiome, which was still present in whole MWTS comprised several genera including Pseudomonas, Acinetobacter, Clostridium, and Mycobacterium, that contain species that are opportunistic pathogens, suggesting a potential threat for mineral water microbiology safety. This study is the first to investigate the bacterial community of a full-scale mineral water treatment plant in China. The results provided data regarding the bacteria composition and dynamics in an MWTS, which will contribute to the beneficial manipulation of the mineral water microbiome.

A novel method: using an adenosine triphosphate (ATP) luminescence-based assay to rapidly assess the biological stability of drinking water

The rapid and credible evaluations of the microbial stability of a drinking water distribution system (DWDS) are of great significance for ensuring the safety of drinking water and predicting microbial pollution. Conventional biostability assessment methods mainly focus on bacterial regrowth or evaluation of the level of nutrients that support bacterial regrowth. However, such methods are time-consuming and have many limitations. An adenosine triphosphate (ATP) assay can rapidly measure all active microorganisms and is known to be a useful method to assess the microbial activity of drinking water. The measurement of ATP has been used for more than a decade in the field of drinking water research. This article reviews the application of an ATP luminescence-based method to assess the biostability of drinking water and discusses the feasibility of ATP measurement as a parameter for quickly evaluating this criterion. ATP measurement will help researchers and water managers better monitor the biological stability of drinking water from the source to the consumer's tap. This review covers the: (1) principle and application of the ATP measurement in drinking water quality assessment; (2) comparison of the merits and demerits of several methods for evaluating the biostability of drinking water; (3) discussions on using ATP measurement in evaluating biostability; and (4) improvements in the use of ATP measurement in evaluating biostability. At the end of this review, recommendations were given for better application of the ATP measurement as a parameter for monitoring the microbial quality of drinking water.

Modulation of fat metabolism and gut microbiota by resveratrol on high-fat diet-induced obese mice

PURPOSE

The antioxidant resveratrol (RSV) has low bioavailability and can reach the colon to access the gut microbial ecosystem. RSV administration together with high-fat diet prevented abnormal changes of intestinal microbiota. However, whether or not RSV can reshape the intestinal microbiota of obese mice and alleviate obesity-related diseases remains to be studied. This study aimed to explore the role of RSV in alleviating high-fat-induced obesity and its relationship with oxidative stress and gut microbiota.

METHODS

Male C57BL/6 mice were divided into five groups and administered for 16 weeks with: standard diet (CON), high-fat diet (60% energy for lard, HFD), and HFD with low, medium, and high dose of RSV, 50, 75, and 100 mg/kg body weight administered daily via drinking water, respectively.

RESULTS

Medium and high RSV treatment significantly prevented body weight gain, decreased relative weight of liver and adipose tissue compared with HFD (P<0.05). All doses significantly prevented HFD-induced increase of serum triglyceride, low density lipoprotein cholesterol, glucose, and endotoxemia (P<0.05). Medium and high dose also prevented chronic inflammation by decreasing serum interleukin-1 and tumor necrosis factor-alpha (P<0.05), and oxidative stress in liver and brain indicated by increase in superoxide dismutase, catalase, glutathione peroxidase activity (P<0.05). Formation of malondialdehyde was prevented by all doses compared with HFD (P<0.05). Both medium and high doses of RES increased alpha diversity of gut microbiota according to the Chao1 and Shannon indices (P<0.05). Medium dose induced obvious shift in gut microbiota composition according to principal component analysis. High dose of RSV effectively prevented HFD-induced increase of Coriobacteriaceae and Desulfovi-brionaceae (P<0.05), which show a significant correlation with body weight (r>0.8 P<0.00).

CONCLUSION

RSV prevented HFD-induced endotoxemia, oxidative stress, and gut microbiota change.

Characterization of the bacterial community composition in water of drinking water production and distribution systems in Flanders, Belgium

The quality of drinking water is influenced by its chemical and microbial composition which in turn may be affected by the source water and the different processes applied in drinking water purification systems. In this study, we investigated the bacterial diversity in different water samples from the production and distribution chain of thirteen drinking water production and distribution systems from Flanders (Belgium) that use surface water or groundwater as source water. Water samples were collected over two seasons from the source water, the processed drinking water within the production facility and out of the tap in houses along its distribution network. 454‐pyrosequencing of 16S ribosomal RNA gene sequences revealed a total of 1,570 species‐level bacterial operational taxonomic units. Strong differences in community composition were found between processed drinking water samples originating from companies that use surface water and other that use groundwater as source water. Proteobacteria was the most abundant phylum in all samples. Yet, several phyla including Actinobacteria were significantly more abundant in surface water while Cyanobacteria were more abundant in surface water and processed water originating from surface water. Gallionella, Acinetobacter, and Pseudomonas were the three most abundant genera detected. Members of the Acinetobacter genus were even found at a relative read abundance of up to 47.5% in processed water samples, indicating a general occurrence of Acinetobacter in drinking water (systems).

Long-term spatial and temporal microbial community dynamics in a large-scale drinking water distribution system with multiple disinfectant regimes

Long-term spatial-temporal investigations of microbial dynamics in full-scale drinking water distribution systems are scarce. These investigations can reveal the process, infrastructure, and environmental factors that influence the microbial community, offering opportunities to re-think microbial management in drinking water systems. Often, these insights are missed or are unreliable in short-term studies, which are impacted by stochastic variabilities inherent to large full-scale systems. In this two-year study, we investigated the spatial and temporal dynamics of the microbial community in a large, full scale South African drinking water distribution system that uses three successive disinfection strategies (i.e. chlorination, chloramination and hypochlorination). Monthly bulk water samples were collected from the outlet of the treatment plant and from 17 points in the distribution system spanning nearly 150 km and the bacterial community composition was characterised by Illumina MiSeq sequencing of the V4 hypervariable region of the 16S rRNA gene. Like previous studies, Alpha- and Betaproteobacteria dominated the drinking water bacterial communities, with an increase in Betaproteobacteria post-chloramination. In contrast with previous reports, the observed richness, diversity, and evenness of the bacterial communities were higher in the winter months as opposed to the summer months in this study. In addition to temperature effects, the seasonal variations were also likely to be influenced by changes in average water age in the distribution system and corresponding changes in disinfectant residual concentrations. Spatial dynamics of the bacterial communities indicated distance decay, with bacterial communities becoming increasingly dissimilar with increasing distance between sampling locations. These spatial effects dampened the temporal changes in the bulk water community and were the dominant factor when considering the entire distribution system. However, temporal variations were consistently stronger as compared to spatial changes at individual sampling locations and demonstrated seasonality. This study emphasises the need for long-term studies to comprehensively understand the temporal patterns that would otherwise be missed in short-term investigations. Furthermore, systematic long-term investigations are particularly critical towards determining the impact of changes in source water quality, environmental conditions, and process operations on the changes in microbial community composition in the drinking water distribution system.

Effect of disinfectant residual on the interaction between bacterial growth and assimilable organic carbon in a drinking water distribution system

Public health is threatened by deteriorated water quality due to bacterial regrowth and uncontrolled growth-related problems in drinking water distribution systems (DWDSs). To investigate the scope of this problem, a two-year field study was conducted in south China. The amount of assimilable organic carbon (AOC), total cell concentrations (TCC), and intact cell concentrations (ICC) of water samples were determined by flow cytometry. The results indicated that ICC was significantly correlated to AOC concentration when the chlorine concentration was less than 0.15 mg/L, and ICC was lower at chlorine concentrations greater than 0.15 mg/L, suggesting that free chlorine level had effect on AOC and ICC. To further analyze the effect of disinfectant on AOC and bacterial growth, we designed an orthogonal experiment with different dosages of two commonly used disinfectants, chlorine and chloramine. The results demonstrated that high concentrations of free chlorine (＞0.15 mg/L) and chloramine (＞0.4 mg/L) were associated with relatively low proportions of intact cells and cultivable bacteria. Compared with chlorine, chloramine tended to cause lower AOC level and intact cells, likely because the chlorinated disinfection byproducts (DBPs) were more easily absorbed by bacteria than the chloraminated DBPs. Based on the statistical analysis of 240 water samples, ICC was limited when AOC concentration was less than 135 μg/L, while temperature and the number of small-size particles showed positive effects on ICC (P＜0.05). We conclude that the use of chloramine and controlling particle numbers should be suitable strategies to limit bacterial regrowth.

Spatiotemporal changes in bacterial community and microbial activity in a full-scale drinking water treatment plant

To gain insight into the bacterial dynamics present in drinking water treatment (DWT) systems, the microbial community and activity in a full-scale DWT plant (DWTP) in Guangzhou, South China, were investigated using Illumina Hiseq sequencing analyses combined with cultivation-based techniques during the wet and dry seasons. Illumina sequencing analysis of 16S rRNA genes revealed a large shift in the proportion of Actinobacteria, Proteobacteria and Firmicutes during the treatment process, with the proportion of Actinobacteria decreased sharply, whereas that of Proteobacteria and Firmicutes increased and predominated in treated water. Both microbial activity and bacterial diversity during the treatment process showed obvious spatial variation, with higher levels observed during the dry season and lower levels during the wet season. Clustering analysis and principal component analysis indicated dramatic shifts in the bacterial community after chlorination, suggesting that chlorination was highly effective at influencing the bacterial community. The bacterial community structure of finished water primarily comprised Pseudomonas, Citrobacter, and Acinetobacter, and interestingly showed high similarity to biofilms on granular activated carbon. Additionally, the abundance of bacterial communities was relatively stable in finished water and did not change with the season. A large number of unique operational taxonomic units were shared during treatment steps, indicating the presence of a diverse core microbiome throughout the treatment process. Opportunistic pathogens, including Pseudomonas, Acinetobacter, Citrobacter, Mycobacterium, Salmonella, Staphylococcus, Legionella, Streptococcus and Enterococcus, were detected in water including finished water, suggesting a potential threat to drinking-water safety. We also detected bacteria isolated from each treatment step using the pure-culture method. In particular, two isolates, identified as Mycobacterium sp. and Blastococcus sp., which belong to the phylum Actinobacteria, were obtained from finished water during the dry season. Together, these results provided evidence of spatial and temporal variations in DWTPs and contributed to the beneficial manipulation of the drinking water microbiome.

Community Structure Analysis and Biodegradation Potential of Aniline-Degrading Bacteria in Biofilters

Aniline has aroused general concern owing to its strong toxicity and widespread distribution in water and soil. In the present study, the bacterial community composition before and after aniline acclimation was investigated. High-throughput Illumina MiSeq sequencing analysis illustrated a large shift in the structure of the bacterial community during the aniline acclimation period. Bacillus, Lactococcus, and Enterococcus were the dominant bacteria in biologically activated carbon before acclimation. However, the proportions of Pseudomonas, Thermomonas, and Acinetobacter increased significantly and several new bacterial taxa appeared after aniline acclimation, indicating that aniline acclimation had a strong impact on the bacterial community structure of biological activated carbon samples. Strain AN-1 accounted for the highest number of colonies on incubation plates and was identified as Acinetobacter sp. according to phylogenetic analysis of the 16S ribosomal ribonucleic acid gene sequence. Strain AN-1 was able to grow on aniline at pH value 4.0-10.0 and showed high aniline-degrading ability at neutral pH.

The function of advanced treatment process in a drinking water treatment plant with organic matter-polluted source water

To understand the relationship between chemical and microbial treatment at each treatment step, as well as the relationship between microbial community structure in biofilms in biofilters and their ecological functions, a drinking water plant with severe organic matter-polluted source water was investigated. The bacterial community dynamics of two drinking water supply systems (traditional and advanced treatment processes) in this plant were studied from the source to the product water. Analysis by 454 pyrosequencing was conducted to characterize the bacterial diversity in each step of the treatment processes. The bacterial communities in these two treatment processes were highly diverse. Proteobacteria, which mainly consisted of beta-proteobacteria, was the dominant phylum. The two treatment processes used in the plant could effectively remove organic pollutants and microbial polution, especially the advanced treatment process. Significant differences in the detection of the major groups were observed in the product water samples in the treatment processes. The treatment processes, particularly the biological pretreatment and O₃-biological activated carbon in the advanced treatment process, highly influenced the microbial community composition and the water quality. Some opportunistic pathogens were found in the water. Nitrogen-relative microorganisms found in the biofilm of filters may perform an important function on the microbial community composition and water quality improvement.

Bacteria in drinking water sources of a First Nation reserve in Canada

Approximately 20% of the 600 First Nations reserves across Canada are under a drinking water advisory, often due to unacceptable levels of bacteria. In this study, we detected fecal bacteria at an alarmingly high frequency in drinking water sources in a fly-in First Nations community, most notably in buckets/drums of homes without running water where Escherichia coli levels ranged from 20 to 62,000CFU/100mL. The water leaving the water treatment plant was free of E. coli and its free residual chlorine concentration (0.67mg/L) was within the range typically observed for treated water in Canada. Water samples from taps in homes served by cisterns, and those sampled from the water truck and community standpipe, always showed unacceptable levels of E. coli (1 to 2100CFU/100mL) and free residual chlorine concentrations below the 0.2mg/L required to prevent bacterial regrowth. Samples from taps in homes served by piped water had lower levels of E. coli (0 to 2CFU/100mL). DNA- and RNA-based 16S rRNA Illumina sequencing demonstrated that piped and cisterns water distribution systems showed an abundance of viable cells of Alphaproteobacteria indicative of biofilm formation in pipes and cisterns. The alpha diversity, based on observed OTUs and three other indices, was lowest in water truck samples that supplied water to the cistern and the low free residual chlorine concentration (0.07mg/L) and predominance of Betaproteobacteria (63% of viable cells) that were immediately detected after the truck had filled up at the water treatment plant was indicative of contamination by particulate matter. Given these findings, First Nation residents living without running water and relying on inadequate water distribution systems are at higher risk of contracting water-born illnesses. We urge all governments in Canada to expand their investments in supporting and sustaining water as a human right in Canada's First Nations communities.

Microbial Diversity of Source and Point-of-Use Water in Rural Haiti - A Pyrosequencing-Based Metagenomic Survey

Haiti endures the poorest water and sanitation infrastructure in the Western Hemisphere, where waterborne diseases cause significant morbidity and mortality. Most of these diseases are reported to be caused by waterborne pathogens. In this study, we examined the overall bacterial diversity of selected source and point-of-use water from rural areas in Central Plateau, Haiti using pyrosequencing of 16s rRNA genes. Taxonomic composition of water samples revealed an abundance of Firmicutes phyla, followed by Proteobacteria and Bacteroidetes. A total of 38 bacterial families and 60 genera were identified. The presence of several Klebsiella spp. (tentatively, K. pneumoniae, K. variicola and other Klebsiella spp.) was detected in most water samples. Several other human pathogens such as Aeromonas, Bacillus, Clostridium, and Yersinia constituted significantly higher proportion of bacterial communities in the point-of-use water samples compared to source water. Bacterial genera traditionally associated with biofilm formation, such as Chryseobacterium, Fusobacterium, Prevotella, Pseudomonas were found in the point-of-use waters obtained from water filters or domestic water storage containers. Although the pyrosequencing method utilized in this study did not reveal the viability status of these pathogens, the abundance of genetic footprints of the pathogens in water samples indicate the probable risk of bacterial transmission to humans. Therefore, the importance of appropriate handling, purification, and treatment of the source water needed to be clearly communicated to the communities in rural Haiti to ensure the water is safe for their daily use and intake.

Understanding, Monitoring, and Controlling Biofilm Growth in Drinking Water Distribution Systems

In drinking water distribution systems (DWDS), biofilms are the predominant mode of microbial growth, with the presence of extracellular polymeric substance (EPS) protecting the biomass from environmental and shear stresses. Biofilm formation poses a significant problem to the drinking water industry as a potential source of bacterial contamination, including pathogens, and, in many cases, also affecting the taste and odor of drinking water and promoting the corrosion of pipes. This article critically reviews important research findings on biofilm growth in DWDS, examining the factors affecting their formation and characteristics as well as the various technologies to characterize and monitor and, ultimately, to control their growth. Research indicates that temperature fluctuations potentially affect not only the initial bacteria-to-surface attachment but also the growth rates of biofilms. For the latter, the effect is unique for each type of biofilm-forming bacteria; ammonia-oxidizing bacteria, for example, grow more-developed biofilms at a typical summer temperature of 22 °C compared to 12 °C in fall, and the opposite occurs for the pathogenic Vibrio cholerae. Recent investigations have found the formation of thinner yet denser biofilms under high and turbulent flow regimes of drinking water, in comparison to the more porous and loosely attached biofilms at low flow rates. Furthermore, in addition to the rather well-known tendency of significant biofilm growth on corrosion-prone metal pipes, research efforts also found leaching of growth-promoting organic compounds from the increasingly popular use of polymer-based pipes. Knowledge of the unique microbial members of drinking water biofilms and, importantly, the influence of water characteristics and operational conditions on their growth can be applied to optimize various operational parameters to minimize biofilm accumulation. More-detailed characterizations of the biofilm population size and structure are now feasible with fluorescence microscopy (epifluorescence and CLSM imaging with DNA, RNA, EPS, and protein and lipid stains) and electron microscopy imaging (ESEM). Importantly, thorough identification of microbial fingerprints in drinking water biofilms is achievable with DNA sequencing techniques (the 16S rRNA gene-based identification), which have revealed a prevalence of previously undetected bacterial members. Technologies are now moving toward in situ monitoring of biomass growth in distribution networks, including the development of optical fibers capable of differentiating biomass from chemical deposits. Taken together, management of biofilm growth in water distribution systems requires an integrated approach, starting from the treatment of water prior to entering the networks to the potential implementation of "biofilm-limiting" operational conditions and, finally, ending with the careful selection of available technologies for biofilm monitoring and control. For the latter, conventional practices, including chlorine-chloramine disinfection, flushing of DWDS, nutrient removal, and emerging technologies are discussed with their associated challenges.

Spatiotemporal variation of planktonic and sediment bacterial assemblages in two plateau freshwater lakes at different trophic status

Both planktonic and sediment bacterial assemblages are the important components of freshwater lake ecosystems. However, their spatiotemporal shift and the driving forces remain still elusive. Eutrotrophic Dianchi Lake and mesotrophic Erhai Lake are the largest two freshwater lakes on the Yunnan Plateau (southwestern China). The present study investigated the spatiotemporal shift in both planktonic and sediment bacterial populations in these two plateau freshwater lakes at different trophic status. For either lake, both water and sediment samples were collected from six sampling locations in spring and summer. Bacterioplankton community abundance in Dianchi Lake generally far outnumbered that in Erhai Lake. Sediment bacterial communities in Erhai Lake were found to have higher richness and diversity than those in Dianchi Lake. Sediments had higher bacterial community richness and diversity than waters. The change patterns for both planktonic and sediment bacterial communities were lake-specific and season-specific. Either planktonic or sediment bacterial community structure showed a distinct difference between in Dianchi Lake and in Erhai Lake, and an evident structure difference was also found between planktonic and sediment bacterial communities in either of these two lakes. Planktonic bacterial communities in both Dianchi Lake and Erhai Lake mainly included Proteobacteria (mainly Alpha-, Beta-, and Gammaproteobacteria), Bacteroidetes, Actinobacteria, Cyanobacteria, and Firmicutes, while sediment bacterial communities were mainly represented by Proteobacteria (mainly Beta- and Deltaproteobacteria), Bacteroidetes, Chlorobi, Nitrospirae, Acidobacteria, and Chloroflexi. Trophic status could play important roles in shaping both planktonic and sediment bacterial communities in freshwater lakes.

Impact of disinfection on drinking water biofilm bacterial community

Disinfectants are commonly applied to control the growth of microorganisms in drinking water distribution systems. However, the effect of disinfection on drinking water microbial community remains poorly understood. The present study investigated the impacts of different disinfectants (chlorine and chloramine) and dosages on biofilm bacterial community in bench-scale pipe section reactors. Illumina MiSeq sequencing illustrated that disinfection strategy could affect both bacterial diversity and community structure of drinking water biofilm. Proteobacteria tended to predominate in chloraminated drinking water biofilms, while Firmicutes in chlorinated and unchlorinated biofilms. The major proteobacterial groups were influenced by both disinfectant type and dosage. In addition, chloramination had a more profound impact on bacterial community than chlorination.

Influence of substrate type on microbial community structure in vertical-flow constructed wetland treating polluted river water

Microorganisms attached on the surfaces of substrate materials in constructed wetland play crucial roles in the removal of organic and inorganic pollutants. However, the impact of substrate material on wetland microbial community structure remains unclear. Moreover, little is known about microbial community in constructed wetland purifying polluted surface water. In this study, Illumina high-throughput sequencing was applied to profile the spatial variation of microbial communities in three pilot-scale surface water constructed wetlands with different substrate materials (sand, zeolite, and gravel). Bacterial community diversity and structure showed remarkable spatial variation in both sand and zeolite wetland systems, but changed slightly in gravel wetland system. Bacterial community was found to be significantly influenced by wetland substrate type. A number of bacterial groups were detected in wetland systems, including Proteobacteria, Chloroflexi, Bacteroidetes, Acidobacteria, Cyanobacteria, Nitrospirae, Planctomycetes, Actinobacteria, Firmicutes, Chlorobi, Spirochaetae, Gemmatimonadetes, Deferribacteres, OP8, WS3, TA06, and OP3, while Proteobacteria (accounting for 29.1-62.3 %), mainly composed of Alpha-, Beta-, Gamma-, and Deltaproteobacteria, showed the dominance and might contribute to the effective reduction of organic pollutants. In addition, Nitrospira-like microorganisms were abundant in surface water constructed wetlands.

Environmental (Saprozoic) Pathogens of Engineered Water Systems: Understanding Their Ecology for Risk Assessment and Management

Major waterborne (enteric) pathogens are relatively well understood and treatment controls are effective when well managed. However, water-based, saprozoic pathogens that grow within engineered water systems (primarily within biofilms/sediments) cannot be controlled by water treatment alone prior to entry into water distribution and other engineered water systems. Growth within biofilms or as in the case of Legionella pneumophila, primarily within free-living protozoa feeding on biofilms, results from competitive advantage. Meaning, to understand how to manage water-based pathogen diseases (a sub-set of saprozoses) we need to understand the microbial ecology of biofilms; with key factors including biofilm bacterial diversity that influence amoebae hosts and members antagonistic to water-based pathogens, along with impacts from biofilm substratum, water temperature, flow conditions and disinfectant residual—all control variables. Major saprozoic pathogens covering viruses, bacteria, fungi and free-living protozoa are listed, yet today most of the recognized health burden from drinking waters is driven by legionellae, non-tuberculous mycobacteria (NTM) and, to a lesser extent, Pseudomonas aeruginosa. In developing best management practices for engineered water systems based on hazard analysis critical control point (HACCP) or water safety plan (WSP) approaches, multi-factor control strategies, based on quantitative microbial risk assessments need to be developed, to reduce disease from largely opportunistic, water-based pathogens.